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CHEMICAL ENGINEERING METHODS AND TECHNOLOGY

CHEMISTRY AND CHEMICAL ENGINEERING RESEARCH PROGRESS

No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services.

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CHEMICAL ENGINEERING METHODS AND TECHNOLOGY

CHEMISTRY AND CHEMICAL ENGINEERING RESEARCH PROGRESS

A.K. HAGHI EDITOR

Nova Science Publishers, Inc. New York

Copyright © 2010 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Chemistry and chemical engineering research progress / editor, A.K. Haghi. p. cm. Includes index. ISBN 978-1-61942-237-7 (eBook) 1. Composite materials. 2. Chemistry. 3. Chemical engineering. I. Haghi, A. K. TA418.9.C6C444 2009 660--dc22 2010015594

Published by Nova Science Publishers, Inc.

New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

vii Using Accelerated Ageing Process to Predict the Archival Life of Cellulose Nitrate Based Materials and Historical Objects A. Hamrang

1

Degradation Studies of Cellulose Esters Using Peak Ratio Measurement Technique A. Hamrang

9

HIPing of Encapsulated Electrically Conductive ZrO2-based Composites Sedigheh Salehi, Omer Van der Biest, Jef Vleugels, Marc de Prez Alfons Bogaerts and Patrick Jacquot Nanoparticle Finishes Influence on Color Matching of Cotton Fabrics G. Rosace, V. Migani, C. Colleoni, M.R. Massafra and E. Sancaktaroglu Removal of Chromium(VI) Ion From Aqueous Solutions Using Acid Modified Rice Husk S.M. Mirabdolazimi, A. Mohammad-Khah, R. Ansari and M.A. Zanjanchi Lattice Parameters of Calcite in the PT-Plane to 7.62 kbar and 533°C Michael J. Bucknum and Eduardo A. Castro

17

29

45

55

vi Chapter 7

Chapter 8

Contents A Closer Perspective of Processing and Properties of Swing Threads Ashkay Kumar and M. Subramanian Senthil Kannan

67

Impact of Different Stages of Yarn Spinning Process on Fibre Orientation and Properties of Ring, Rotor and Air-jet Yarns Ashkay Kumar and S.M. Ishtiaque

89

Chapter 9

Y2O3-Nd2O3 Double Stabilized Zro2-Ticn (60/40) Nano-Composites S. Salehi, K. Vanmeensel, B. Yüksel, O. Van der Biest, and J. Vleugels

137

Chapter 10

Y2O3 And Nd2O3 Co-Stabilized Zro2-WC Composites Sedigheh Salehi, Omer Van der Biest and Jef Vleugels

151

Chapter 11

Electro-Conductive Zro2-Nbc-Tin Composites Using Nbc Nanopowder Made By Carbo-Thermal Reaction S. Salehi, J. Verhelst, O. Van der Biest, J. Vleugels

161

On the Pyrolysis of Polymers as a Petrochemical Feedstock Recovery Route S. M. Al-Salem and P. Lettieri

175

Chapter 12

Index

231

PREFACE The collection of topics in this book aims to reflect the diversity of recent advances in chemistry and chemical engineering with a broad perspective which may be useful for scientists as well as for graduate students and engineers. This new book presents leading-edge research from around the world in this dynamic field. Diverse topics published in this book are the original works of some of the brightest and well-known international scientists. The book offers scope for academics, researchers, and engineering professionals to present their research and development works that have potential for applications in several disciplines of engineering and science. Contributions ranged from new methods to novel applications of existing methods to gain understanding of the material and/or structural behavior of new and advanced systems. Contributions are sought from many areas of science and engineering in which advanced methods are used to formulate (model) and/or analyze the problem. In view of the different background of the expected audience, readers are requested to focus on the main ideas, and to highlight as much as possible the specific advantages that arise from applying modern ideas. A chapter may therefore be motivated by the specific problem, but just as well by the advanced method used which may be more generally applicable. I would like to express my deep appreciation to all the authors for their outstanding contribution to this book and to express my sincere gratitude for their generosity. All the authors eagerly shared their experiences and expertise in this new book. Special thanks go to the referees for their valuable work. Professor A. K. HAGHI Montréal, CANADA [email protected]

In: Chemistry and Chemical Engineering Reserch Progress ISBN: 978-1-61668-502-7 Editor: A.K. Haghi © 2010 Nova Science Publishers, Inc.

Chapter 1

USING ACCELERATED AGEING PROCESS TO PREDICT THE ARCHIVAL LIFE OF CELLULOSE NITRATE BASED MATERIALS AND HISTORICAL OBJECTS A. Hamrang* Consultant to the Polymeric Industries, England, UK

ABSTRACT Accelerated ageing process was used to estimate the useful lives of cellulose nitrate based materials in archival conditions. Samples in glass containers were aged at 15-50% relative humidity conditions and at different temperatures. The extent of degradation was measured by the time for cellulose nitrate to lose 20% of its relative viscosity. The data obtained were plotted against the reciprocal temperature using the Arrhenius relationship. Extrapolation of the data to room temperature (20oC) gave approximate archival lives of samples. Even at temperatures below their second glass transition temperatures (Tg), cellulose nitrates deteriorated significantly in humid environments; the degree of which depended on the level of humidity. The importance of these results in relation to the archival conditions is discussed.

INTRODUCTION Problems regarding decomposition of cellulose nitrate based historical objects in museums and various collections are quite serious. These problems are characterised by the release of plasticiser deposits on the surface of objects as well as loss of colour, surface crazing, etc. The loss of plasticiser is evident as a heavy liquid / crystalline deposit. The properties and applications of the cellulose nitrate materials are dependent on their degrees of nitration. For plastic grade nitrates [1], the nitrogen content is between 10.7-11.1 percent and their degrees of esterification are between 1.9-2.0. Cellulose nitrate with a nitrogen content of less than 11.1 percent is the least flammable and is used for production of *

Email: [email protected]

2

A. Hamrang

celluloid. Celluloid is the cellulose nitrate which is plasticized with camphor. Celluloid was the first man made plastic to be used by artists [2]. The first recorded use of celluloid in sculpture (Constructed Head No.3, 1917-20) is now in the Museum of Modern Art, New York. The most popular period of use for celluloid was between 1900-1935. The material was used because of its characteristics such as rigidity, toughness, transparency of basic composition as well as forming multi coloured sheets. The history of celluloid invention and usage are described elsewhere [3-4]. Several studies have been carried out on the decomposition of cellulose nitrates at elevated temperatures [5-7] and a few of them with emphasis on hydrolysis [8-9]. However these studies have been carried out mainly at high temperatures (>100oC) which museum objects and other collections will not be kept at. The thermal sensitivity of nitrate esters is such that they are readily cleaved at ambient temperatures to generate nitrogen oxide. Nitrogen oxide is highly oxidising and an odd electron molecule which can initiate highly exothermic, free radical reactions [10]. This oxidising atmosphere will result in the production of carboxylic acid groups which may then undergo oxidative decarboxylation, particularly in the presence of metal ions. Due to thermal sensitivity of cellulose nitrates, in this work accelerated ageing was carried out at temperatures below 90oC (i.e. 50-80oC) and at four different levels of humidity (i.e. 15-50%). The effect of ageing process on samples was monitored by viscometric analyses.

EXPERIMENTAL Materials The original samples used in this work were in the form of uniform plastic sheet of tortoiseshell effect and 1.2 mm in thickness. No information was available on the history of production or the plasticizer used in the sample. No visible signs of degradation such as stickiness, surface crazing, loss of colour or odour were noticed. The original samples were characterised by various methods. Direct solution method [11] was used to isolate the plasticiser from the polymer matrix and analysed. The plasticizer content was measured at about 29% which is a usual amount for fabricated cellulose nitrate materials. FTIR studies revealed that natural camphor was the plactiser used for these samples. The second glass transition temperature (Tg) of the samples was also measured by Differential Scanning Calorimetry (DSC) technique, which was found to be about 53oC. This corresponded well with the Tg of undegraded cellulose nitrate materials mentioned in references [12].

Ageing Conditions The samples were aged in all glass containers with the desired environments simulated within them. The ageing processes were carried out at temperatures of 50, 60, 70, 80oC and

Using Accelerated Ageing Process to Predict the Archival Life of Cellulose …

3

in15, 30, 40, 50% relative humidity conditions. The samples were taken out periodically for analysis.

Viscometry Viscometric analyses were carried out for the original samples and the aged samples in order to examine if degradation is taking place and at what rate. Viscometric measurements were performed by determining the flow times using an Ostwald Viscometer type BS/U/M2. Flow times of a fixed volume of both a polymer solution and pure solvent were determined from which the relative viscosity could be found. A 1% solution of cellulose nitrate sample in acetone was prepared, for all viscometric analyses. All the calculations are based on the average of 3 tests for each sample. A modified Arrhenius approach was adopted and the time taken for 20% loss in relative viscosity determined rather than a rate constant.

RESULTS AND DISCUSSION Arrhenius Treatment In order to extrapolate the high temperature ageing results to normal archival conditions the data were treated by the Arrhenius approach. The rate constant for a first order reaction from classical kinetics is given by:

K=

2 .3 ⎡ a ⎤ log ⎢ t ⎣ a − x ⎥⎦

Here ‘a’ is the initial concentration of the reactant and ‘x’ is the decrease in the concentration of the reactant after time ‘t’. It is assumed that the reaction is first order [13-14]. In this work ‘a’ is the initial physical property of the sample (viscosity retention), ‘a-x’ is the remaining property after a given time, ‘t’. The rate constant for a first order reaction can be calculated from the time required for the property to decrease to half the original value (halftime life, thalf) by the equation shown below.

thalf

=

2.3 log 2 K

Using Arrhenius relationship, extrapolation of the reaction rates to other temperatures can be made as shown below.

d ln K E = dT RT 2

4

A. Hamrang

where ‘E’ is the activation energy, ‘T’ is the absolute temperature and ‘R’ is the gas constant. The rate constants obtained at two or more temperatures are plotted as ln K against

1 . In this way a straight line is obtained which then it can be extrapolated to the desired T temperature.

Archival Predictions Figures 1 to 4 show the times for a 20% loss in relative viscosity of cellulose nitrate materials at a series of elevated temperatures (50-80oC). In these figures reciprocal temperatures were plotted versus number of days taken for a sample to lose 20% of its original relative viscosity value at a particular relative humidity condition. Reciprocal temperatures were calculated as (1 / T+273) where T is the four ageing temperatures of 50, 60, 70 and 80oC. At each relative humidity condition and at each ageing temperature one value was obtained for example in Figure 1, at 15% relative humidity and at 50, 60, 70, 80oC, it took 111, 56, 20 and 5 days respectively for nitrates to lose 20% of their relative viscosity values. For Figures 2 to 4 the same procedures were followed. Prediction of life under archival conditions can be made by extrapolating the plots. Figures 1 to 4 examine the effects of ageing on cellulose nitrate materials at 15, 30, 40 and 50% relative humidity conditions, respectively. Linear plots were obtained and as expected the rate of degradation increasing with increasing temperatures. One significant result is that the degradation rate is greater at higher humidity levels. This effectively illustrates the hydrolytic effect of moisture in the degradation mechanism even at a relatively lower temperature of 50oC. It is evident that changes took place in the polymer structure as a result of exposure to different temperatures and humidity levels. Temperatures greater than 50oC are likely to be above the Tg of cellulose nitrate materials. Above the Tg penetration of moisture into the polymer structure will occur more easily. In addition the Tg of cellulose nitrate polymer will be lower in the presence of moisture due to the swelling of the polymer. This will facilitate the penetration of water and its chemical reaction with the polymer. From the data, it is possible to determine the approximate lifetime for cellulose nitrate made objects through modification of the Arrhenius expression assuming that the rate of degradation follows the first order kinetics. It should be pointed out that the rate controlling step in the degradation of the plastic grade nitrates may be more complex than first order as there may be interactions between the main polymer and the additives used. In this work the time taken for the nitrate samples to achieve 20% loss in relative viscosity are plotted against 1 = 0.0034 ). the reciprocal temperature in K and the data extrapolated to 20oC (i.e. 273 + 20 The least squares method was used in each case to obtain the best fit for the points.


5

15% Relative Hum idity

Time for 20% Loss in Relative Viscosity (Days)

10000

1000

100

10

1 0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

1 / T (K) Figure 1. Time for 20% loss in relative viscosity of cellulose nitrates versus the reciprocal temperature of ageing (K) at 15% relative humidity condition.

A. Hamrang

6



10000

1000

100

10

1 0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

1 / T (K)

Figure 2. Time for 20% loss in relative viscosity of cellulose nitrates versus the reciprocal temperature of ageing (K) at 30% relative humidity condition.



10000

1000

100

10

1 0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

1 / T (K)

Figure 3. Time for 20% loss in relative viscosity of cellulose nitrates versus the reciprocal temperature of ageing (K) at 40% relative humidity condition.


7



10000

1000

100

10

1 0.0027

0.0028

0.0029

0.003

0.0031

0.0032

0.0033

0.0034

1 / T (K) Figure 4. Time for 20% loss in relative viscosity of cellulose nitrates versus the reciprocal temperature of ageing (K) at 50% relative humidity condition.

From figures 1 to 4, it is estimated that at 20oC (0.0034 on X axis), the cellulose nitrate based object will lose 20% of its property after 8.22, 5.45, 4.11 and 2.74 years at 15, 30, 40 and 50% relative humidity conditions, respectively. According to the above data, it is clear that cellulose nitrate polymers are sensitive to temperature. Humidity also affects cellulose nitrate materials even at ambient temperatures.

CONCLUSION The conditions that the cellulose nitrate based objects are kept in play a vital role in their archival longevity. By means of accelerated ageing trials, the useful lives of these objects can be estimated. Predicting the archival lives of cellulose nitrate objects by using modified Arrhenius expression can only be taken as approximations. Whilst considering the effect of plasticizer and the environmental conditions, accelerated ageing results indicated that

8

A. Hamrang

humidity plays an important part in the degradation process of cellulose nitrate based materials and objects. As the level of humidity increased, degradation process occurred at a faster rate. Therefore, according to the data obtained in this study, it would be necessary to minimise the level of humidity as low as possible in order to prolong the useful life of the cellulose nitrate based objects in actual archival conditions.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Saunders, K. J., Organic Polymer Chemistry, Chapman & Hall Ltd., 1973, P255. Katz, S., Plastics / Designs and Materials, Macmillan Publishing Co. Inc., 1978, P4244. Kaufman, M., The first Century of Plastics, Crown Press, 1963. Worden, E. C., Nitrocellulose Industry, Van Nostrand, Vols. 1 and 2, 1911. Philips, L., Nature, 160, 753, (1947) Miles, F. D., Cellulose Nitrate, Interscience, 1955, P253. Adams, G. K., and Bawn, C. E. H., The Homogeneous Decomposition of Ethyl Nitrate, Transactions of the Faraday Society, 45, (1949), P494. Miles, F. D., Cellulose Nitrate, Oliver & Boyd, 1955, P286. Ott, E., Spurlin, H. M., and Grafflin, M. W., Cellulose and Cellulose Deravatives, 2nd ed., Part II, Interscience Publishers, 1954, P1052. Miles, F. D., Cellulose Nitrate, Oliver & Boyd, 1955, P263-4. Crompton, T. R. Chemical Analysis of Additives in Plastics, 2nd ed., Pergamon Press, 1977, Chapter 1. Brydson, J. A., Plastic Materials, 3rd ed., Butterworth Group, 1975, P493-494. Adelstein, P. Z., McCrea, J. L., J. Soc. Photog. Sci and Eng., 7, (1981), 6. Ram, A. T., McCrea, J. L., Presented at the 129th SMPTE Technical Conference, Los Angeles, CA, (1987).


Chapter 2

DEGRADATION STUDIES OF CELLULOSE ESTERS USING PEAK RATIO MEASUREMENT TECHNIQUE A. Hamrang* ASenior Consultant of Polymer Industries, 4 Heswall Avenue, Withington, Manchester, M20 3ER, UK

ABSTRACT Aspects of degradation of plastic grade cellulose esters have been investigated with work concentrating on cellulose nitrate and cellulose acetate. The original samples were characterized and used as controls for subsequent ageing studies. Relative rates of degradation for samples aged in various temperatures and relative humidities were evaluated using FTIR studies, with emphasis on Peak Ratio Measurements (PRM) technique. In this study for nitrates the peak ratios corresponding to C=O (1730 cm-1) / NO2 (1650 cm-1) and OH (3400 cm-1) / NO2 (1650 cm-1) were measured. For acetates C=O (1750 cm-1) / CH3 (1370 cm-1) and OH (3490 cm-1) / CH3 (2935 cm-1) were measured. The results obtained from this technique along with visual observations of samples indicated that the rate of deacetylation / denitration (de-esterification) depended on moisture concentration. These reactions are largely characteristics of surrounding relative humidity and temperature of cellulose esters. The results indicated that for nitrates, denitration is accompanied by the formation of carbonyl impurities whilst for acetates carbonyl impurities and deacetylation did not occur together and deacetylation is the major process of degradation.

INTRODUCTION Plastic grade cellulose esters are susceptible to degrading processes as a consequence of the chemical nature of the cellulose chain molecules and the substituents along the chain. The rate of degradation is dependent upon the type and degree of substitution of the individual polymer. Primary decomposition processes slowly produce degradation products and if they *

Email: [email protected]

10

A. Hamrang

are not removed, they can (catalytically) cause a faster and more extensive degradation. Autocatalytic oxidation and hydrolysis reactions occur in cellulose esters. For cellulose nitrates, it has been suggested that auto-oxidation is the more likely degradation mechanism. [1] They are readily cleaved at ambient temperatures to generate nitrogen oxide, which is highly oxidising and acts as an odd electron molecule capable of initiating highly exothermic free radical reactions. It is indicated in some other studies [2-4] that the highly oxidising atmosphere produced by the release of nitrogen oxide will eventually result in the production of carboxylic acid groups and these can undergo oxidative decarboxylation, particularly in the presence of metal ions. Although degradation would proceed faster in the presence of oxygen than in an inert atmosphere, the change of atmosphere would have no influence on the nature of volatile products. In contrast to cellulose nitrates, cellulose acetates are much more stable to thermal degradation. Cellulose acetate is quite resistant to oxidative degradation, even at rather high temperature of 90oC, but if the temperature is sufficiently high, for instance 160oC, then it will oxidise and as a result, a loss of strength, change of colour and solubility changes occur. [5]. Various studies [6-9] have indicated that primary decomposition products are environmentally dependent. In the presence of oxygen a different degradation mechanism is involved, since the first evolved degradation product in air is carbon dioxide, but in inert atmosphere (i.e. Helium), it is acetic acid. The reaction of cellulose acetate with acetic acid and water has been investigated and the results showed a slow and complex reaction of two simultaneous reversible second order processes taking place. [10] It was concluded that in the system, degradation occur as a result of acetic acid hydrolysis. It was also found that the rate of the reaction is temperature dependent and under ambient conditions the acetylation of the C6 acetyl group in the polymer chain is one of the primary decomposition processes. Most of the degradation studies carried out by various researchers on cellulose esters are at temperatures above 100oC. In view of this finding, degradation studies in this work were carried out at temperatures near the Tg of the samples (i.e. 50-60oC for nitrates and 100oC for acetate samples) and at 0, 100% humidities. The effect of degradation on samples was monitored by FTIR using PRM technique.

EXPERIMENTAL Materials The original samples used in this work included fabricated cellulose nitrate (CN, manufacturer not known) and cellulose acetate (CA, manufactured by Courtaulds, UK) plastic sheets, with no visible signs of degradation on them. The thickness of CN and CA sheets was measured at 1.2 and 3 mm respectively. The original samples were characterized and used as controls for subsequent ageing processes.

Degradation Studies of Cellulose Esters Using Peak Ratio Measurement

11

Ageing Conditions Strips of samples were aged in all glass containers with the desired environments simulated within them. Anhydrous calcium chloride and distilled water were used to produce 0% and 100% relative humidity (RH) conditions, respectively. The lids were put on tightly and the containers then placed in constant temperature ovens at 50-60oC for CN and 100oC for CA samples. Samples were taken out periodically and analysed.

Sample Characterization All control samples were found to be soluble in acetone. Later on it was revealed that severely degraded samples particularly those aged in high humidity and temperatures became insoluble in acetone. Differential Scanning Calorimetry (DSC) was used to measure the second glass transition temperature (Tg) of the control samples in air. A Mettler furnace with a TC10TA processor was used for this purpose (a sample of about 20mg was used at a constant rate of 15oC). In these analyses, the Tg of CN and CA control samples were measured at 53oC and 117oC, respectively which corresponded well with the figures reported in references [11-12] for undegraded samples. FTIR spectroscopy was also used for characterizing samples, the details of which are described below.

FTIR Analyses – PRM Technique All control and aged samples were dissolved in acetone and thin films cast at < 0.01 mm thickness. A Nicolet Magna 560 FTR Spectrometer was used to record all spectra (spectra obtained using 64 scans at a resolution of 4 cm-1). The effects of ageing on samples were monitored by FTIR-PRM technique and the changes, which took place, were recorded. The affected bands of the aged samples were compared against the control samples. In this technique, peak heights were measured, because if bands overlap, using peak heights may give more reproducible results since only the centre positions of the bands are used.

RESULTS AND DISCUSSION There are several regions of interest in the characteristic transmittance bands at 4000-400 cm-1 for CN and CA samples. These bands occurred mainly due to the vibrations produced by the cellulose ring, ether linkages and substituent groups, details of which are discussed elsewhere. [13] A few of these regions are of prime importance with respect to degradation. These are associated with denitration / deacetylation (de-esterification) reactions. For CN samples, these IR regions correspond to C6-nitroester (NO2; at 1650 cm-1), carbonyl impurities (C=O at 1730 cm-1) and OH (at 3400 cm-1) vibrations. For CA samples these regions of interest correspond to CH3 (of COCH3 occurring at 1370 cm-1, 2935 cm-1), (C=O at 1750 cm-1) and (OH at 3490 cm-1).

12

A. Hamrang

In this study for nitrates, the peaks which corresponded to C=O / NO2 and OH / NO2 ratios were chosen for measurement. For acetates peak ratios of OH / CH3 and C=O / CH3 were measured. Figures 1 to 5 show the results of peak ratio measurements carried out for CN and CA samples aged in both dry and humid conditions at various temperatures. Figures 1 and 2 examine the effects of ageing on CA samples at 0, 100% relative humidity (RH) and 100oC. The results in Figure 1 corresponding to peak ratio OH / CH3 for CA samples showed a progressive increase in values as the severity of ageing process increased. This could be due to the formation of acetic acid (CH3COOH) inside the ageing containers. The rate of acid formation occurred at a faster rate in humid conditions. This was also evident by the strong vinegary smell detected for acetate samples, particularly for those aged in humid environments. As a result of this very rapid reaction, the samples aged in humid conditions became insoluble in acetone in a much shorter period (i.e. about 20 weeks), compared with those aged in dry conditions (i.e. more than 80 weeks). The most significant result here is that the degradation rate is greater at 100% RH, rather than 0% RH and effectively illustrates the hydrolytic effect of moisture in the degradation mechanism.

Figure 1. Values measured for peak ratio of OH / CH3 versus ageing time for CA samples aged at 0, 100oC & 0% RH.

The results of measurements for peak ratio of C=O / CH3 are presented in Figure 2. These results indicated that as the ageing time increased the measured values decreased. This may indicate that carbonyl impurities are not formed in this case. Also these results may be the indication that the losses in acetyl groups may be occurring as a result of deacetylation. This could also indicate that deacetylation and the formation of carbonyl impurities may not be happening together and deacetylation is the major degradation process.


13

Figure 2. Values measured for peak ratio C=O / CH3 versus ageing time for CA samples aged at 100oC & 0% and 100% RH.

Figures 3 to 5 examine the effects of ageing on CN samples at 0, 100% relative humidity and 50-60oC. Figures 3 and 5 show the results of the measurements carried out for the OH / NO2 ratio. Figure 3 shows the effect of temperature and Figure 5, the effect of moisture on CN samples. As the severity of ageing conditions increased, the values for the measured ratio decreased. This may be due to the reduction of OH and NO2 groups. In humid environments the reduction in values occurred at a much faster rate, indicating that the loss of covalent nitrate groups in the presence of moisture accelerated. This could be responsible for changes in solubility characteristics and loss of properties for CN samples, as the samples aged in humid conditions became insoluble in acetone (i.e. in less than 10 weeks of ageing), whilst samples aged in dry conditions retained their solubility characteristics and most of their useful properties even after a long ageing process (i.e. over 60 weeks of ageing).

Figure 3. Values measured for peak ratio of OH / NO2 versus ageing time for CN samples aged at 50, 60oC and 0% RH.

14

A. Hamrang

Figures 4 and 5 show the results of the peak measurements carried out for C=O / NO2 ratio. Here the measured values increased for samples aged in both dry and humid conditions. The increase in values was larger for samples aged in humid environments. These results showed a progressive increase in the carbonyl / nitroester ratio, as the samples became more degraded. This indicated that as denitration occurred (decrease in OH / NO2 ratio), the rate of formation of carbonyl impurities increased (increases in C=O / NO2 ratio).

Figure 4. Values measured for peak ratio of C=O / NO2 versus ageing time for CN samples aged at 50, 60oC and 0% RH.

Figure 5. Values measured for peak ratio of OH / NO2 versus ageing time for CN samples aged at 60oC & 0% and 100% RH.


15

CONCLUSION The results obtained in this study indicated that the peak ratio measurement technique could be used to monitor the changes in polymeric systems of cellulose esters, which may occur as a result of degradation. The rate of degradation of cellulose acetates and cellulose nitrates are environmentally dependent. The increase in moisture concentration can increase the rate of degradation. The results showed that the degradation process for acetates is accompanied by the loss in acetyl groups which may be occurring as a result of deacetylation. These results also indicated that the formation of carbonyl impurities did not occur together with deacetylation. Therefore, deacetylation is the major process of degradation for cellulose acetates. In contrast to acetates, for cellulose nitrates, denitration is accompanied by the formation of carbonyl impurities.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Miles, F. D., Cellulose Nitrate, Oliver & Boyd, 1955, P263-264. Hon, D. N. S. & Gui, T. L., Photodegradation of Cellulose Nitrate, Polymer Photochemistry, 7 (1986), P299-310. Ott, E. & Spurlin, H. M., Cellulose and Cellulose Derivatives, Vol. V, Part II, Interscience Publishers, 1954, P1036. Miles, F. D., Cellulose Nitrate, Oliver & Boyd, 1955, P158-9. Evans, E. F. & McBurney, L. F., Ind. Eng. Chem., 41 (1949), P1260. Zitomer, F., Anal. Chem., 40 (1968), P1091-5. Scotney, A., The thermal Degradation of Cellulose Triacetate-I, The Reaction Products, Europ. Polym. J., 8 (1972), P163-174. Scotney, A., The thermal Degradation of Cellulose Triacetate-II, The Carbonaccous Residues, Europ. Polym. J., 8 (1972), P175-184. Scotney, A., The thermal Degradation of Cellulose Triacetate-III, The Degradation Mechanism, Europ. Polym. J., 8 (1972), P185-193. Hiller, L. A., The Reaction of Cellulose Acetate With Acetic Acid and Water, J. Polymer. Sci., 10 (1953), P385-423. Brydson, J. A., Plastic Materials (3rd ed.), Butterworth Group, 1975, P493-4. Brydson, J. A., Plastic Materials (2nd ed.), Iliffe Books Ltd. 1969, P369. Haslam, J. & Willis, H. A. & Squirrell, D. C. M., Identification and Analysis of Plastics (2nd ed.), Iliffe Books, 1972, P534-6.


Chapter 3

HIPING OF ENCAPSULATED ELECTRICALLY CONDUCTIVE ZRO2-BASED COMPOSITES Sedigheh Salehi1, Omer Van der Biest1, Jef Vleugels1, Marc De Prez2, Alfons Bogaerts2, and Patrick Jacquot2 1

Department of Metallurgy and Materials Engineering, K.U.Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium 2 Bodycote HIP, Industriepark Noord 7, B-9100 Sint-Niklaas, Belgium

ABSTRACT Yttria-stabilised ZrO2 can be pressureless sintered in air at 1450°C. The addition of 40 or 50 vol % electrically conductive secondary phases however makes it impossible to reach closed porosity by means of pressureless sintering under protective atmosphere, whereas full density can be obtained by hot pressing or pulsed electric current sintering at 1450°C. Densification at higher temperature strongly reduces the toughness and consequently strength of the composite material due to ZrO2 grain growth, eventually leading to spontaneous phase transformation and material degradation. Therefore, as an alternative, the possibility of post HIPing and encapsulated HIPing of ZrO2-based composites with 40 or 50 vol % WC, NbC or TiN is investigated. Encapsulated HIPing of ceramics at temperatures above 1550°C is commonly performed using quartz encapsulation. The target temperature of 1420°C however is below the softening point of SiO2, rendering this type of material unsuitable. Moreover, glass compositions with a suitable softening point are not commercially available. In order to find a solution, two potential encapsulation approaches were investigated. The first was to coat the cold isostatically pressed ZrO2-based composite powder compacts with a 1-2 mm thick ZrO2 powder coating prior to sinter-HIP. The ZrO2 coating reaches closed porosity at a temperature of about 1300°C before applying the pressure. This approach allowed full densification of the ZrO2-based composites at 1420°C. The main problem however was to remove the ZrO2 coating from the sample. A solution was found in using a very thin layer of boron nitride powder in-between the composite powder compact and the external ZrO2 powder coating, resulting in a spontaneous coating degradation during cooling. In another approach, low carbon steel was used for vacuum encapsulation, using Al2O3 powder to fill the gap between the powder compact and the steel tube capsule.

18

Sedigheh Salehi, Omer Van der Biest, Jef Vleugels et al. The microstructures and mechanical properties of the HIPed samples (1420°C, 30min, 170 MPa) are compared with those after hot pressing (1450°C, 1h, 30MPa).

1. INTRODUCTION ZrO2 ceramics are known for their high fracture toughness due to the transformation toughening mechanis [1] Addition of hard, conductive secondary phases such as TiN [2], NbC [3] or WC [4] increases the modest hardness of ZrO2 whilst keeping the high toughness and excellent strength. The addition of hard secondary phases allows engineering a new generation of ceramics with mechanical properties that fill the gap between those of the tough and strong cermets (ceramic-metal composites) and the high hardness carbides, nitrides or borides, as schematically presented in Figure 1. The large-scale production of complex shaped ceramic parts that can not be densified by pressureless sintering, however is challenging due to the difficulty in creating a homogeneous high temperature and pressure during densification. Hot Isostatic Pressing (HIP) however can be used as a solution. In HIP, rigid tools with limited strength and simple geometry (like graphite dies in hot pressing) are avoided since high isostatic pressures (~100-300 MPa) are established by an applied gas pressure. Due to the applied high pressure during sintering, it is possible to densify materials at temperatures lower than during conventional hot pressing. The reduced sintering temperature allows to control and avoid grain growth [5-7], increasing the material’s strength[8]. Amongst the advantages of HIPing are: increased density, healing of major processing flaws, achieving more reproducible properties, improving or even producing novel microstructures, elevated material strength and in general the possibility to process large and complex parts at reduced cost. Conventional HIPing usually involves a post HIPing of moulded or sintered parts. An essential requirement for this method is that the component should have closed porosity [9]. In the case of ZrO2 based composites, post HIPing can result in ZrO2 grain growth and consequently tetragonal to monoclinic phase transformation that is accompanied by microcrack formation. In ZrO2-based ceramic composites, there is a tendency to keep the yttria stabilizer content as low as possible, because a tetragonal ZrO2 with lower yttria content allows obtaining a higher toughness. This however makes ZrO2 ceramics more sensitive to a post heat treatment. The post HIPing method is verified in this paper. An alternative HIP technique is sinter-HIPing, a two-step process involving sintering at low pressure or in vacuum to closed porosity, immediately followed by a HIP process at elevated pressure. In this method, no intermediate cooling and manipulation is necessary between the sintering and HIP treatment. A series of pressureless sintering tests on ZrO2based composites with 40 vol% NbC, WC or TiN revealed that the minimum temperature needed to achieve closed porosity was 1550°C for ZrO2-TiN and 1650°C for ZrO2-NbC or ZrO2-WC. These high temperatures however are not appropriate because a sintering temperature above 1500°C increases the risk of ZrO2 grain growth and crack formation due to ZrO2 phase transformation. Another way of direct HIPing of green ceramic parts uses encapsulation. Capsules prevent pressurizing gas from entering pores and components with open porosity. The important issue is to find a suitable capsule that can fulfil the requirement of being plastically deformable at the HIP temperature in order to transfer the gas pressure uniformly to the

HIPing of Encapsulated Electrically Conductive ZrO2-based Composites

19

sample, being thermally stable at the HIP temperature. Quartz encapsulation is commonly used for HIPing above 1500°C. A final method is the sinter-canning technique, which involves applying a coating of highly sinterable powder mixture to the green component [10]. The powder coating should reach closed porosity during heating up in vacuum before applying the isostatic pressure. The powder mixture should have a good matching thermal expansion with that of the component, to avoid cracking during heating.

(A)

(B) Figure 1. Fracture toughness versus hardness (a) and hardness versus modulus of rupture (b) for the ZrO2 based composites and a range of common ceramic classes [2, 4, 13].

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Sedigheh Salehi, Omer Van der Biest, Jef Vleugels et al.

This work focuses on the encapsulation and sinter-canning techniques. With respect to encapsulation, two types of materials are widely used. Sheet metal containers of mainly mild steel, stainless steel or nickel based alloys are used at low temperatures. Stainless steel for example can be used as capsule to HIP alumina nanopowder at 1350°C [11]. At higher temperatures, e.g. 1500-2000°C, glass encapsulation is commonly used [12]. In a preliminary set of experiments, commercially available quartz and borosilicate glass were used to encapsulate ZrO2-based composites for HIPing at 1420°C. Quartz however did not deform at this temperature and the melting point of borosilicate glass was too low resulting in a very low capsule viscosity. As a possible solution, yttria-stabilised ZrO2 powder was chosen as coating material (sinter-canning technique) due to the relatively low onset point of densification (~1300°C, pressureless). CIPed (Cold Isostatically Pressed) composite powder compacts were coated with a 1-2 mm thick ZrO2 powder coating prior to sinter-HIP. The ZrO2 coating reaches closed porosity at about 1400°C, before applying the pressure, allowing to fully densify ZrO2-based composites with 40 vol % secondary hard phases at 1420°C. In a further attempt, a boron nitride coating was added to the ZrO2 coating, to facilitate coating removal. In another approach, low carbon steel was used for vacuum encapsulation, using Al2O3 powder to fill the gap between the powder compact and the steel tube capsule.

2. EXPERIMENTAL PROCEDURE Three ZrO2-based compositions were chosen for HIPing experiments, i.e., 1.75 mol% yttria stabilized ZrO2-TiN (60/40 vol%), 2 mol% yttria stabilized ZrO2-WC (60/40 vol%) and 2 mol% yttria stabilized ZrO2-NbC with 40 or 50 vol% NbC. Details on the starting powders and powder preparation method are provided elsewhere [2-4]. The powder mixtures were sieved (315 mesh) prior to cold isostatically pressing in a cylindrical mould (φ~3 cm, H~4 cm) at 300 MPa (EPSI, Temse, Belgium). In case of sinter canning, ZrO2 powder (Tosoh grade TZ-3Y, Japan) with a thickness of 1-2 mm was applied to the green compact by means of a second CIP treatment. After initial composite sample CIPing, the compacted powder was removed from the mould, reinserted in a ZrO2 powder bed and CIPed at 300 MPa. To facilitate application of a double boron nitride (BN) + ZrO2 coating, a spherical sample geometry was used (Figure 2). The composite powder mixture was poured in a selfmade mould using silicone moulding rubber (Castaldo, MA, USA) with spherical shape. After filling the mould with powder, the two parts of the rubber mould were sealed with a banderol, packed in a balloon and CIPed at 300 MPa.


21

Figure 2. Rubber mould and balloon used for making spherical BN+ZrO2 coated samples.

The CIPed composite was plunged in BN (HeboFill, Henze, Germany) powder before immersion into the ZrO2 powder bed prior to the second CIP cycle. Steel encapsulation was realised by encapsulating spherical CIPed composite samples in a low carbon steel tube using Al2O3 powder as protective bed around the sample inside the tube. All steel encapsulated, ZrO2 and BN+ZrO2 coated compacts were HIPed at Bodycote (Sint-Niklaas, Belgium) in a molybdenum heated HIP furnace. The HIP cycle is presented in Figure 3. In step 1, the compacts are heated at 5°C/min in an argon pressure of 0.2-0.3 MPa (2-3 bar) up to 1250°C. In step 2, the pressure is decreased to 2 × 10-3 MPa (2E-2 bar) at 1250°C and the samples are heated further at 5°C/min. In order to allow the ZrO2 coating to reach closed porosity, the samples were soaked at 1420°C for 1 h at 2 × 10-3 MPa before applying 170 MPa argon gas pressure. The dwell time at maximum temperature and pressure is 30 minutes. The samples were naturally cooled under reduced pressure during the cooling step (step 3). After removal of the encapsulation, the microstructure and mechanical properties of the ceramics were investigated and compared with those of hot pressed samples. Hot pressing was always performed at 1450ºC for 1 h under 30 MPa pressure. Microstructural investigation was performed by scanning electron microscopy (SEM, XL-30FEG, FEI, Eindhoven, The Netherlands). The density of the samples was measured in ethanol, according to the Archimedes method (BP210S balance, Sartorius AG, Germany). The Vickers hardness, HV10, was measured (Model FV-700, Future-Tech Corp., Tokyo, Japan) with an indentation load of 98 N and a dwell time of 10 s. The indentation toughness, KIC, was calculated according to the formula of Anstis et al. [3] based on the radial crack pattern produced by Vickers HV10 indentations. The reported values are the mean and standard deviation of 5 measurements.

Sedigheh Salehi, Omer Van der Biest, Jef Vleugels et al.

1

2

30 min

1600 Temperature (°C)

3 P:170

(2) T:1420°C

180 150

1200

1h

120 90

800

60 400 0

T:1250

(P:0.2,0.3) 0

(P:-0.002)

Pressure (MPa)

22

30 0

50 100 150 200 250 300 350 400

Time (min) Figure 3. Applied HIP cycle for the powder coated composites.

3. RESULTS AND DISCUSSION 3.A. Post HIPing As a start, hot pressed (1450°C, 30 MPa, 1h) 1.75 mol % yttria stabilized ZrO2-TiN (60/40 vol %) composites were additionally hot isostatically pressed (1390°C, 20 min, 140 MPa Ar) to investigate the influence of the additional heat treatment on the microstructure and mechanical properties. The mechanical properties are summarised in Table 1 and the microstructures are shown in Figure 4, revealing that the post HIPing resulted in a significant grain growth of the TiN phase. Therefore, the softer ZrO2 phase will also show substantial grain growth. ZrO2 grain growth is accompanied with microcrack formation due to tetragonal to monoclinic phase transformation and consequently leads to decreasing hardness (see Table 1). Microcracking is a toughening mechanism that can be added to the other active toughening mechanisms, i.e., transformation toughening and crack deflection, explaining the increased fracture toughness. Due to the substantial grain growth and associated microcracking and loss of hardness, it was concluded that post HIPing, even at temperature of 1390ºC is not an option to pursue.


23

(A)

(B) Figure 4. Hot pressed (1450°C, 1h, 30 MPa) ZrO2-TiN (60/40), before (left) and after (right) HIP. TiN = dark, ZrO2 = grey, WC = white (originating from the milling medium).

Table 1. Mechanical properties of hot pressed (1450°C, 30MPa, 1h) ZrO2-TiN before and after HIPing

Hardness (GPa) Toughness (MPa.m0.5)

Before HIP 13.29 ± 0.13 6.0 ± 0.3

After HIP 12.49 ± 0.09 6.5 ± 0.4

3.B. Powder Coating Encapsulation 3.B.1. ZrO2 Coating The HIPed 2 mol% yttria stabilized ZrO2-NbC (60/40 vol%) samples before and after capsule removal are shown in Figure 5. The ZrO2 capsules, were removed by Electro Discharge Machining (EDM). A necessary condition for a material to be electro-erodable is a low enough electrical resistivity (< 5µΩ.m). ZrO2 is an electrical insulator (109 Ω.m) and can not be processed by ED [14]. Hence, in order to be able to remove the capsule by EDM, a

2 24

Sedigheh Salehi, S Omer Van V der Biest, Jef Vleugells et al.

rootating diamon nd wheel was used to makee a groove in the ZrO2 coatting down to the t electrocoonductive ZrO O2-based com mposite materiial. Wire-EDM M allowed too machine a cylindrical shhape and cut-off the crackeed coating. The T ZrO2 coatting is cracked because of the higher thhermal expanssion coefficiennt of the ZrO2 compared to the composite, resulting inn a stronger shhrinkage of th he ZrO2 coatiing during coooling and thee concomitant formation of o too high teensile stresses in the coatingg. Although thhese tensile strresses are subsstantial, the cooating does noot delaminate due to the exccellent bondinng between thee coating and the t composite substrate. t ZrO2-baseed compositess with 40 vol% % TiN or NbC could be suuccessfully Although the deensified by HIPing H at 14200°C in 170 MPa M argon (seee Figure 6. d and f), the ZrO2-NbC ceeramic with 50 vol% NbC could not (seee Figure 6.b). The microstrructure of the HIPed and hoot pressed ZrO O2-NbC and ZrO Z 2-TiN (60/440) grades are similar, as shhown in Figuree 6.c-f).

Fiigure 5. HIPed ZrO2 powder cooated compositees before and affter capsule rem moval; the ZrO2 coating crracked during cooling.

Table 2. Mecchanical prop perties of HIP Ped (1420°C, 170 1 MPa, 30 min) and Hott pressed (1450°C, 1h, 30MPa) 2 mol% m yttria sttabilized ZrO O2-NbC (50/500 and 60/40) and a 1.75 mol% yttria stabilized d ZrO2-TiN (60/40) compoosites Hot pressed M Material gradee ZrO2-NbC (50 Z 0/50) Z 2-NbC (60 ZrO 0/40) Z 2-TiN (60/40) ZrO

HV10 Pa) (GP 15.666 ± 0.08 13.774 ± 0.19 13.770 ± 0.07

HIPed KIC10 (MPa.m0.5) 5.6 ± 0.3 5.0 ± 0.3 5.6 ± 0.1

HV10 (GPa) porous 14.99 ± 0.26 13.45 ± 0.12

KIC C10 (MP Pa.m0.5) / 5.7 ± 0.4 5.3 ± 0.1


25

Figure 6. SEM microstructures of Hot pressed (left) and HIPed (ZrO2 coating capsule) (right) 2 mol% yttria stabilized ZrO2-NbC (50/50) (a,b), 2 mol% yttria stabilized ZrO2-NbC (60/40) (c,d) and 1.75 mol% yttria stabilized ZrO2-TiN (60/40) (e,f) composites. The ZrO2 phase is dark in the ZrO2-NbC and bright in the ZrO2-TiN composites. Black phase is Al2O3 which was added to all compositions (0.75 wt %) as ZrO2 grain growth inhibitor.

3.B.2. BN+ZrO2 coating Because of the difficulty in removing the cracked ZrO2 coating, a dual BN + ZrO2 coating was tested. The idea was to weaken the interfacial strength between the ZrO2 coating and the composite substrate resulting in a spontaneous coating delamination during cooling. The HIPed BN+ZrO2 coated ZrO2-WC (60/40) composite before and after coating removal are shown in Figure 7. The ZrO2 capsule could be easily manually removed with a spatula. The hardness, toughness and density of the HIPed and hot pressed grades are similar, as shown in Table 3, proving that the dual BN+ZrO2 coating technique is quite suitable for sinter-HIPing of ZrO2-based composites at 1420°C.

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Sedigheh Salehi, S Omer Van V der Biest, Jef Vleugells et al.

Fiigure 7. HIPed ZrO2 + BN coaated 2 mol% yttrria stabilized ZrrO2-WC (60/400) before (a) andd after (b) ZrrO2 capsule rem moval.

perties of 1.755 mol% Y2O3 stabilized ZrrO2-TiN (60/440) and 2 Table 3. Mecchanical prop mol% Y2O3 sta m abilized ZrO2-WC (60/40)) composites, hot pressed at a 1450°C forr 1 h under 30 MPa and HIPed at 14420°C under 170MPa for 30 min Hot presssed M Material grade

density (g/cm3)

Z 2 -TiN (60/4 ZrO 40)

5.81

Z 2-WC (60/4 ZrO 40)

9.80

HV10 (GPa) 13.77 ± 0.20 16.53 ± 0.20

HIPed KIC10 (MPa.m0.5)

density (g/cm3)

5.4 ± 0.3

5.83

7.5 ± 0.3

9.77

HV10 H ( (GPa) 13.41 ± 0 0.13 16.18 ± 0 0.16

KIC10 (MPa.m0.5 ) 5.6 ± 0.2 7.5 ± 0.2

3.C. Steel En ncapsulation n In another attempt, the CIPed sphericcal compositee samples werre encapsulateed in a low caarbon steel tub be using alum mina powder as a protective bed b around thee sample insidde the tube. The HIPed steeel encapsulaated and crosss-sectioned sample s are shhown in Figuure 8. The m mechanical pro operties of stteel encapsulaated HIPed (11420°C, 170 MPa, 30 minn) and hot prressed (1450°C, 1 h, 30 MP Pa ) 2 mol% Y2O3 stabiliseed ZrO2-WC (60/40) ( compoosites were foound to be the same, as sum mmarized in Taable 4.

(A)

( (B)

Fiigure 8. Overvieew (a) and crosss-section (b) off the steel encappsulated HIPed 2 mol% yttria stabilized s ZrrO2-WC (60/40 0) composite.


27

Table 4. Mechanical properties of hot pressed (1450°C, 1 h, 30 MPa ) and HIPed (1420°C, 170 MPa, 30 min, using low carbon steel encapsulation) 2 mol% Y2O3 stabilised ZrO2-WC (60/40) composites Hot pressed HV10 density (g/cm3) (GPa) ZrO2WC (60/40)

9.80

16.53 ± 0.20

KIC10 (MPa.m0.5)

HIP density (g/cm3)

HV10 (GPa)

KIC10 (MPa.m0.5)

7.5 ± 0.3

9.81

16.03 ± 0.14

7.1 ± 0.4

4. CONCLUSION ZrO2-based composites with 40 vol% TiN, NbC or WC addition could be successfully HIPed (sinter canning) using a ZrO2 coating. In order to facilitate the ZrO2 capsule removal after HIPing, a thin BN powder coating was applied in-between the composite compact and the ZrO2 powder coating. The result was successful, since the capsule could be manually removed easily and the mechanical properties of the HIPed materials (90 min at 1420°C of which 30 min at 170 MPa Ar) were similar to those of hot-pressed grades (60 min at 1450°C and 30 MPa). Alternatively, low carbon steel encapsulation using Al2O3 powder as a protective powder bed around the CIPed composite sample can be used. The mechanical properties of the steel encapsulated HIPed and hot pressed grades were the same. Post HIPing of hot pressed ZrO2-TiN (60/40) at 1390°C was resulted to a decrease in hardness due to ZrO2 grain growth and associated microcracking; therefore post HIPing option was not further investigated.

ACKNOWLEDGMENTS S. Salehi expresses her thanks to the Research Council of K.U.Leuven for a doctoral scholarship (DB/07/012). This work was supported by the Commission of the European Communities within the Framework 6 Program under project No. STRP 505541-1.

REFERENCES [1] [2] [3]

R. H. J. Hannink, P. M. Kelly, and B. C. Muddle, Transformation toughening in Zirconia-Containing ceramics, J. Amer. Ceram. Soc., 83 (2000) 461-487. S. Salehi, O. Van der Biest and J. Vleugels, Electrically conductive ZrO2-TiN composites, J. Europ. Ceram. Soc., 26 (2006) 3173–3179. S. Salehi, J. Verhelst, O. Van der Biest, J. Vleugels, Electro-conductive ZrO2-NbC composites using NbC nanopowder made by carbo-thermal reduction, Proceedings of 30th International conference on advanced ceramics and composites, Daytona Beach, Jan 2007.

28 [4]

[5] [6]

[7] [8] [9]

[10] [11]

[12]

[13] [14]

Sedigheh Salehi, Omer Van der Biest, Jef Vleugels et al. G. Anné, S. Put, K. Vanmeensel, D. Jiang, J. Vleugels, O. Van der Biest, Hard, tough and strong ZrO2-WC composites from nanosized powders., J. Europ. Ceram. Soc., 25 (2005) 55-63. R. Widmar, Future prospect for Hot isostatic pressing; Proceedings of the Third International Conference Osaka, Japan, June 1991, p. 3. N. Hoo, F. H. Fores, Synthesis of a 8-TiAl alloy by mechanical alloying and hot isostatic pressing, Proceedings of the International Conference on Hot Isostatic Pressing, 20-22 May 1996, Andover, Massachusetts, USA, p. 91. L. Delaey, H. Tas; Proceedings of the International Conference on Hot Isostatic Pressing- HIP ’93 Antwerp, Belgium, 21-23 April 1993. Seong-Min Choi, Hideo Awaji, Nanocomposites - a new material design concept; Science and Technology of Advanced Materials, 6 (2005) 2–10. R. Davidge, J. Sleurs and L. Buekenhout; HIPing of technical ceramics: A synopsis; Proceedings of International Conference on Hot Isostatic Pressing of Materials: Application and developments, Antwerp 25th-27th April 1988. p. 5.1 Sheehan, J. E., Cermet fabrication with thermal spraying and hot isostatic pressing, Ceramic Engineering Science Proc., 4 (1983) 695. P. Weimar, R. Knitter, D. V. Szabo, Densification of nanosized alumina powders by Hot Isostatic Pressing, Proceedings of The International Conference on Hot Isostatic Pressing, 20-22 May 1996, Andover, Massachusetts, USA, p. 105. H. V. Atkinson and B. A. Rickinson; Hot isostatic pressing, The Adam Hilger series on new manufacturing processes and materials, imprint by IOP publishing Ltd, Bristol, UK, 1991. Cambridge Materials Selector, CMS version 2.05, Granta Design Ltd., UK, 1994. R. Morrell, Handbook of properties of technical & engineering ceramics, 1985, p. 95166.


Chapter 4

NANOPARTICLE FINISHES INFLUENCE ON COLOR MATCHING OF COTTON FABRICS G. Rosace1*, V. Migani1, C. Colleoni1, M.R. Massafra2, and E. Sancaktaroglu3 Dipartimento di Ingegneria Industriale - Università degli Studi di Bergamo - viale Marconi, 5 - 24044 Dalmine (BG) – Italy 2 Stazione Sperimentale per la Seta - via G. Colombo, 83 - 20133 Milano – Italy 3 Department of Textile Engineering – Uludag University – Gorukle Campus, 16059 Bursa – Turkey 1

ABSTRACT Color change is one of the most important side effects of textile treatments to be considered. This research focuses on color modifications occurring ondyed cotton fabrics due to the nanoparticle sized dendrimer (DWR), dendrimer-fluorocarbon (DWOR) and fluorocarbon (FWOR) finishing. A remarkable influence of finishing onto ΔR (reflectance difference) and ΔE (color difference) of fabrics was observed. Roughness of treated surfaces also plays a relevant role in determining the reflectance and colour changes. In fact, roughness increases the scattering of light thus decreasing surface reflectance. Finishes particle sizes designate the distribution and orientation of surface roughness and the overlay of their absorbance values in the short wavelength results in color differences. Thanks to the nanoparticle size, the highest performances are achieved in some typical textile finishing applications: water and oil repellency induced by finishing on cotton textile and mechanical characteristics of the fabric have been here deeply investigated.

1. INTRODUCTION Cotton is one of the major textile fibers and it has a unique combination of properties, including softness, durability, high strength, good dyeability and biodegradability, and for * Corresponding author: phone +39 035 2052021; fax +39 035 2052077 e-mail: [email protected]

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G. Rosace, V. Migani, C. Colleoni et al.

many centuries it has found use in textile production [1].Reactive dyes with vinylsulphone groups are widely used to dye cotton fibers, because of the simplicity of application, the great choice of commercial products and their cheapness.Even though a long tradition has given a solid and an in-depth knowledge of cotton textile fibers and of dyeing processes, the new research borders are moving to a development of the inherent textile materials properties: for this purpose, chemical finishing procedures are widely used. Textile materials can be treated with different functional finishes, such as water and oil repellent, durable press, soil-release, flame retardant, antistatic, and antimicrobial [2,3]. Water repellent finishing on fabrics is mostly imparted by the incorporation of low surface energy compounds, accompanied by the increase of the contact angle of liquids on its surface. The most recent approaches to improverepellency are based on the use of nanoparticles, such ashighly branched 3D surface functional macromolecules called dendrimers, whose effect mechanism depends on being in a position to build-up crystal structures in nano-range, which produce wash-permanent, waterrepellent and highly abrasion resistant effects. When combined with fluoropolymers, dendrimers force them to co-crystallize leading to a self-organization of the whole system and to an enrichment of the fluoro polymers on the most outer layer of the textile [3]. Functionality and properties of dendrimers can be changed by filling their cavities or modifying the core and chain-ends [4]. Conformational flexibility of branches is capable of placing dendrimers hydrophilic interior in contact with aqueous subphase and extending their chains into the air above the air–water interface [5]. Particle size of these repellent finishes plays a vital role because, when the inorganic particle size is reduced, the surface area is increased; this leads to good interaction with the matrix polymer, and a highest performance is achieved [6]. Alteration of surface properties by textile finishing applications and creation of a smoother reflection surface by a reduced superficial particle size could also give a color change [7].In this study the effect of particle sizes on surface roughness and color assessment after finishing of cotton fabrics was evaluated by surface reflectance, absorbance of finishes and color coordinates measurement. For this purpose, three types of commercially available dendrimer water repellent (DWR), fluorocarbon included dendrimer water-oil repellent (DWOR) and fluorocarbon water-oil repellent (FWOR) reagents were impregnated to dyed cotton fabrics and polymerized under optimum conditions. The dyeing of the fabric samples was carried out by three different colors commercial dyes. The reflectance and color coordinates of treated and untreated samples were measured by reflectance spectrophotometer according to the CIELAB, a CIE defined color space, that supports the accepted theory of color perception based on three separate color receptors in the eye (red, green and blue) and is currently one of the most popular color spaces [8].Finally, water and oil repellency performances, treated-substrate characterization and fabrics mechanical properties were extensively investigated to estimate if finishing agents application gives rise to other changes, besides color alterations [9].

Nanoparticle Finishes Influence on Color Matching of Cotton Fabrics

31

2. EXPERIMENTAL 2.1. Fabrics Scoured and bleached woven cotton fabrics (68 g/m2) were employed in this study. Each sample (10 g) was immersed for 30 minutes at 60°C in 5 g/L ECE solution (adetergent free from fluorescent brightening agent, used in the ISO 105 series of color fastness test) with 0.5 g/L soaking agent, in a conical flask with a continuous shaking. The samples were then thoroughly rinsed and dried at room temperature and stored at laboratory conditions (25 ± 2 °C and 65 ± 2% relative humidity).

2.2. Dyes Three different colors commercial Remazol (Dystar) reactive dyes with vinylsulphone groups (Table1) were used. The dyes selection has been made according to the behaviour of finishing chemicals in their maximum reflectance intervals. Table 1. Reactive dyes used Commercial name

λmax

C.I. generic name

Remazol Yellow Gold RNL Remazol Red F3B Remazol Black B

413 541 600

Reactive Orange 107 Reactive Red 180 Reactive Black 5

The molecular structures are reported in Figure 1. All dyes were of commercial grade and were used as received.

A

B

C

Figure 1. A: Reactive Orange 107 (Remazol Yellow Gold RNL). B: Reactive Red 180 (Remazol Red F3B). C: Reactive Black 5 (Remazol Black B).

2.3. Dyeing Agents For level and consistent dyeing of cotton fabrics Bersol CM (1g/L), Berdet WF(1g/L) (sequestering and wetting agents, respectively, supplied by Europizzi - Urgnano, Italy), Depsolube ACA (1g/L) (anti-creasing agent supplied by Basf - Italy) were used. All chemicals were commercial products.

32


2.4. Repellents Patented dendrimer water repellent (density = 1.1 g/cm3), fluorocarbon/dendrimer wateroil repellent (density = 1.03 g/cm3) and also fluorocarbon water-oil repellent (density = 1.03 g/cm3) provided by Rudolf Chemie (Turkey and Italy) were used as finishing agents and coded as DWR, DWOR and FWOR respectively (Table 2). Table 2. Finishing agents codes Textile finish Dendrimer Water Repellent Fluorocarbon/Dendrimer Water-Oil Repellent Fluorocarbon Water-Oil Repellent

Code DWR DWOR FWOR

2.5. Buffer The pH 5.5 buffer used for neutralization after dyeing and finishing application comprised acetic acid (9.60 g dm-3) and sodium acetate (3.56 g dm-3). Chemicals were obtained from Sigma-Aldrich, in analytical grade.

2.6. Dyeing Untreated fabrics were dyed using method depicted in Figure 2, according to selected dyes. Reactive dyeing was carried out using a liquor ratio of 10:1. Samples were then washed, rinsed and neutralized at proper temperature levels, to be finally left to dry under laboratory conditions. 60°C 40 min 20°C

10 min 45 min

10 min B

C

50°C D E

A A= LR 10:1; 1% dye shade; 10 g fabric; 1 g/L Bersol CM; 50 g/L NaCl; 12 g/L Na2CO3; 1 g/L Berdet WE; 1 g/L Depsolube ACA B= rinsing C= 0,7 ml buffer solution (pH= 5,5) D= 1 g/L soaping E= rinsing

Figure 2. Dyeing profile method for reactive dye used.

33

Nano oparticle Finiishes Influencce on Color Matching M of Cotton C Fabricss

2.7. Applicattion of Dend drimers on samples weere padded separately in aqqueous baths with w finishingg chemicals Dyed cotto (D DWR, DWOR R and FWOR R). All produccts were appllied to the faabrics with thhe pad-cure m method, including full immeersion into the bath to a wett pick-up of 600-80% at 20°C C and were cuured at 140-15 50 °C for 1200 seconds. Thee application conditions c forr the three testted finishes arre reported in Table 3: for allproducts a tw wo different cooncentrations were w investigaated, taking innto account thee concentratioon ranges recom mmended by supplier. Table T 3. Dend drimer and flluorocarbon application a conditions Condition ns

DWR

Concentraations (g/l) Pick up (% %) pH Fixation temp t (°C) Fixation time t (min)

100 60-80 5-5.5 150 2

DW WOR 125

300 600-80 5-5.5 1550 2

FWOR 50

30 60-80 5-5.5 150 2

5 50

2.8.Particle Size S Measurrement I The finishes particle sizze measuremeents were perrformed with a Malvern Instruments Mastersizer 200 M 00. During the laser diffracction measurem ment, particlees were passedd through a foocused laser beeam and scatteered light at an angle that was w inversely proportional p too their size. The angular inttensity of the scattered lighht was then measured m by a series of phootosensitive p off these detectoors in the Masstersizer 2000 have been deetectors. The number and positioning opptimized to acchieve maximuum resolution across a broadd range of sizees.

2.9.Textile Testing T GSM (Grams per squaree: the standardd measuremennt of the gravvitational forcee acting on faabrics), TS (Teensile strengthh: the resistannce of a materiial to rupture when subject to tension) annd ELB (Elo ongation at brreak: the incrrease in lenggth when the last componnent of the sppecimen break ks) properties of cotton fabrrics were also measured forr all applicatioons.GSM is a standard meaasurement of fabric f weight per p unit area carried c out for all samples as follows: t size of 20 square cm waas measured by b Mettler balaance (± 10thhe weight of samples with the 4 g The percen g). ntage change of o fabric weighht was calculaated with (1).

(1) where W1 is i the weight of o the substratte after treatm ment and W0 iss the initial weeight of the unntreated substrrate. Tensile strength s and brreaking elongation were meeasured accordding to ISO 133934-1, using g standard testt methods onn dynamometeer Instron Tennsile Tester model m 4501

34


(CRE). Ten specimens were prepared for testing, five for warp direction and five for weft direction. The standard deviations of all experimental results were lower than ± 2,5%.To thoroughly evaluate both water and oil repellency, above mentioned performances were measured after abrasion, washing and iron treatments. The samples were conditioned at 20 ± 2 °C and 65 ± 4 % RH for 24 hours before textile testing, according to standard ISO 139:2005. All measurements were repeated for the three equally treated samples and then averaged. Water and oil repellency tests were reformulated after 5 and 15 repeated home launderings carried out at 40° C, as described in the ISO 6330, followed by tumbler drying at 80° C for 20 min. Half of the samples were also ironed at 150° C for 60 seconds for observation of heat effect on recovery of repellency. The abrading cycles of the treated and control fabric samples were performed on a Nu-Martindale abrasion tester (Mesdan Italy) according to ISO 12947-3 with two different abrasion cycles (150 and 300). Water resistance test measures the resistance to surface wetting, water absorption and penetration. To determine the extent of surface wetting, the ISO 4920 spray test was used. The substrate was held taut within a 15 cm diameter ring at a 45° angle, and 250 mL of water at a temperature of 23 ± 1°C was lightly dropped onto the substrate from a distance of 15.2 cm, to remove excess water. A rating of 80 or higher is desirable, because it indicates better water repellency. Oil repellency was measured according to ISO 14419. In this test, oily drops were deposited onto substrate, allowed to remain for 30 seconds, and removed by wicking or wiping with a paper tissue. Eight different challenge liquids with different liquid tensions are numbered by a rating increasing from 1 in the case of vaseline, the easiest to repel, to 8 in the case of nheptane, the most difficult to repel (Table 4). Oil repellency is reported as the maximum rating of the liquid that does not wet the substrate. For detailed comparisons, multiple drops of each liquid were tested. In general, an oil repellency rating of 5 or higher is desirable. Table 4. Definition of oil repellency Oil repellency rating 8 7 6 5 4 3 2 1

Test liquid n-heptane n-octane n-decane n-dodecane n-tetradecane n-hexadecane 35/65 mix n-hexadecane/vaseline vaseline

γ , mN/M L

19.8 21.4 23.5 24.7 26.4 27.3 29.6 31.5

2.10. Surface Reflectance and Roughness Measurement The reflectance of non-dyed samples (untreated and treated) was measured with a Lambda 950 Perkin Elmer apparatus, equipped with an RSA-PE-150 Labsphere accessory for reflectance measurements. Each reflectance value R (%) was determined as the average of four measurements, with an experimental error of about 1-2%. For a randomly rough surface

35


haaving a Gausssian type surrface heights distribution, the reflectancce can be exxpressed as foollows: p[- (4πσcos i//λ)2] Rr = Rs exp

(2)

s refleectances of perfectly smoooth and roughh surfaces, where Rs and Rr are specular reespectively; σ is the standaard deviation of o the surfacee from its meaan level, funcction of the suurface rough hness; i annd λ are the t incident angle and wavelength of light, reespectively.Ch hanges in surfa face roughnesss of treated fabbrics were exppressed as diffferences in thhe root-mean-square of the vertical Z diimension valuues within thee examined arreas, which w calculated were d using the following equation:

(3)

2.11. Absorb bance Measu urement a spectra of finishees were recordded on a Therm mo Nicolet The ultraviiolet–visible absorption Evolution UV– –Vis 500 specttrophotometerr Vision 32 sooftware, using a 1 cm path length l cell. A spectra werre recorded at room temperaature in the waavelength rangge from 350 too 750 nm at All thhe rate of 300 nm min−1. Finnish/dye soluttions were evaaluated from thhe change of absorbance a att the λmax of th he dye in the UV-Vis U spectraa of the samplle solution.

2.12. Color Difference D A Assessment Color diffeerence evaluation was basedd on the surfacce reflectance in the visible waveband: inndeed, any effe fects that change the reflectaance cause a color c differencce. The color coordinates c off dyed cotton (untreated annd treated) saamples dyestuffs selected for fo dyeing cottton fabrics w were measured d on the same spectrophotom meter used forr absorbance measurements m s, equipped 0 w an integraating sphere with with w a 10mm opening, undder a D65/10 illuminant acccording to IS SO 105 J01. The T spectrophootometer meassurements werre made using the L*a*b* syystem. The evvaluation of th he overall coloor difference (ΔE), ( obtainedd before and after a finishingg, in the 3D coolor space is given g by:

ΔE* =

Δ *) + (Δa *) + (Δb *) (ΔL 2

2

2

(4)

* represents the t lightness difference; d Δaa and Δb, thee differences in a and b where ΔL* vaalues, wherein a* is a measure off redness/greeenness, and b* is a measure m of yeellowness/blueeness.The a* and b* coorddinates approaach to zero foor neutral colors (white, grreys) and incrrease in magnnitude for morre saturated orr intense colorrs. The advanntage of the C CIE-lab system m is that color differences caan be expresseed in units thaat can be relateed to visual peerception and clinical signiificance [8]. Four F reflectance measuremeents were madde on each saample; the saamples were rotated r 90° beefore each measurement, m a the averaages of the and

36

G. Rosace, V. Migani, M C. Coolleoni et al.

reeflectance vallues (%) at wavelengths w b between 400 and 700 nm were recordeed.A white Thermo Nicolet Electronic caalibration platte was used.

3 RESULTSS AND DISC 3. CUSSION 3.1. Particle Size and Su urface Rougghness Meassurements WOR and FWO OR finishing agents are The resultss of nano parrticle sizes foor DWR, DW deepicted in Figu ure 3.DWR prresents the greeatest particle size and voluume (%) valuees are about thhe half of the ones observedd for the two other finishess. Besides, DW WR shows a second s low cooncentration peak p in the parrticles size rannge of 10-100 nm, probablyy due toa self-aassembling off dendrimers [10]. From these resultts, specific surface s areas of nanopartticles were deetermined: 6.6 6 m2/g, 38.0 m2/g and 40.1 m2/g for DWR R, DWOR andd FWOR respeectively.

Fiigure 3. Particlee size of DWR (A), ( DWOR (B B) and FWOR (C C) finishes.

Table 5 co ompares treateed to untreateed samples cooncentrations and RMSxy values, v the laatter computed d using (3). Foor the selectedd chemicals concentrations, the smaller the t particle siize the smooth her the polym mer over the teextile surface, as expected. Particle surfaace area, in faact,increases as a the particle size decreasess: the highest particle surfacce area is achiieved when thhere is a high concentration c of nanometer or sub-nanom meter sized parrticles. This iss the reason w a higher co why oncentration of o DWR produuct is requiredd to obtain thee same repelleency effects off DWOR and FWOR. Surfaace roughness reduces the sppecular reflectance of a wavvelength of ligght, especiallly at high anngle of incideence, and inccreases the sccattering of light l while deecreasing thee surface refflectance. Texxtile sampless treated witth small partticle sized


37

chhemicals, hav ving a higherr surface areea, give a more uniform dispersion, a smoother reeflecting surfaace and thus higher reflectannce values (% %) [8].With thee application of o finishing aggent, it was believed b that such s treatmennt increased thhe inter-yarn and a inter-fibeer frictional foorce, as confirm med by the rooughening effeect on the textiile surface. ble 5. Surfacee characterizaation of untreeated and treaated samples Tab

Samples Untreated DWR DWOR FWOR

Concentratioons (g/l) 0 125 50 50

RMS m (Root-meean-square) nm 25.41 13.7 6.9 6.9

3.2. Repellen ncy Measureements mers have a It was obsserved (Figuree 4) that highh water repelllency degrees of dendrim teendency to im mprove, whenn they are coombined with fluorocarbonn polymers. Itt was also obbserved that untreated u fabrrics showed no n repellency behaviour annd that, for all a different trreatments, watter repellency was initially the same. Affter abrasion and a washing processes p a peerformance decrease d was observed, paarticularly forr lower finishing concenttrations. In adddition, the bin nding propertiies of dendrim mers to textile surface had accceptable fastnnesses.

Fiigure 4. Water repellency r a) affter DWR finishh at 80 g/L and 125 g/L concenntrations, b) DW WOR finish att 30 g/L and 50 g/L concentratiions and c) FW WOR finish at 300 g/L and 50 g/L L concentrationns after: appplication alonee (ref); 150 cyclles of abrasion (A); ( 300 cycless of abrasion (B); laundering (55 cycles) (C C); laundering (5 ( cycles) and irroning (D); launndering (15 cyccles) (E); laundeering (15 cycless) and irooning (F).

38

G. Rosace, V. Migani, M C. Coolleoni et al.

After oil reepellency testting of DWR finishing, no repellency efffect was observed. The poossible reason n is related too the high DWR finishingg surface enerrgy in compaarison with suurface tension of oil (20-35 mN/m). For fluorocarbon f g groups supplieed DWOR andd FWOR, a veery low criticaal energy of 6 mN/m can be b achieved [111]. The channge in oil repeellency was shhown in Figurre 5. The effecct of concentrration is evideent on FWOR R products in comparison c w DWOR products, with p probbably due to the t orientationn of fluorocarrbon chains acchieved by deendrimers. Fo or this reason lower concenntrations of DW WOR are moore efficient thhan FWOR prroducts, which h do not includde dendrimerss [12].

Fiigure 5. Oil repellency after a) DWOR finish at 30 g/L and 50 g/L concentraations and b) FW WOR finish att 30 g/L and 50 g/L concentratiions after: appliication alone (reef); 150 cycles of abrasion (A)); 300 cycles off abrasion (B); laundering l (5 cyycles) (C); launndering (5 cyclees) and ironing (D); ( launderingg (15 cycles) (E E); laundering (15 cycles) and ironing (F).

Despite suffficient fixatioon, textiles finnished with fluuorocarbon suuffer from a clear loss in efffect after waashing, causeed by the unnfavourable coonditions preevailing in thhe washing m machine. Surfa face-active suurfactants, thee extremely polar p medium m (water), thhe elevated teemperature (att least 40°C) in combinationn with the mechanical influuence, lead thee orientated fluorocarbon ch hains “diving away” from thhe edge or beiing very muchh disturbed. After A drying a for this thhe polymer is still on the suubstrate, howeever, but the siide chains aree in disorder, and reeason no oil and a water repeellent effects are a apparent. Since S the fluoorocarbon chaiins melting teemperature is8 80-90°C, the fluorocarbon finish is nott able to sponntaneously reggenerate at rooom or drying temperature. Table 6. 6 Mechanicall properties of o treated fabrrics Cotton C C Concentration (g/l) G GSM (g/m²) W Weight changee (%) Warrp T (N) TS Weft Warrp E ELB (%) Weft

Untreeated 0 66.800 0.0 223.11 144.66 7.6 14.1

DWR 100 70.84 6.0 212.2 85.5 4.5 15.8

125 70.79 6.0 204.5 112.7 3.6 18.0

DWOR D 3 30 6 69.29 3 3.7 2 235.8 1 152.7 4 4.6 2 23.2

50 71.399 6.9 219.33 192.33 5.5 26.0

FWOR 30 69.00 4.0 237.7 154.1 4.7 23.1

50 70.05 6.7 220.4 189.3 5.3 25.0


39

A simple ironing and thus the heating up of the textile over the melting temperature of the fluorocarbon chains would be however sufficient to reorganize the finishing and to reproduce the performance level [11].In our opinion the change in water repellency after washing and abrasion seen on DWR products is also probably related to this reason. Anyway, samples before and after dendrimer and fluorocarbon finishing treatment have very similar mechanical properties as indicated in Table 6 and in a range that is intrinsic to the raw material.

3.3. Color Difference Measurements Color-difference evaluation in the visible waveband (400-700 nm) computed on the basis of (4) is depicted in Figure 6 for the three tested finishes on the cotton fabric samples. It was observed that the application of three finishing products have an effect on color change in any color, whether in hue, chroma, or lightness (AATCC). Color difference trends are comparable for all colors, and always show the highest ΔE value for DWR, while the lowest for FWOR finishing. Besides, distinctive behaviours are observed for red color, which presents the highest ΔE for all finishings, and for blue one, whose attitude is decidedly opposing. Color matching as depicted in Figure 6 and ΔL,* Δa*, Δb* values of dyestuffs selected for dyeing in Table 7 show a remarkable influence of finishing onto color difference of textile. Table 7. ΔL,* Δa*, Δb* values of reactive dyestuffs used on cotton fabrics

ΔL* Colour Yellow Red Blue

DWR 0.40 -0.77 0.34

Δa* DWOR 0.84 0.37 0.28

FWOR 0.80 0.25 -0.39

DWR 0.78 -1.86 -0.46

Δb* DWOR 0.30 -1.29 -0.36

FWOR 0.25 -1.15 0.88

DWR 0.38 -1.01 -0.22

DWOR -0.30 -1.03 -0.15

FWOR -0.29 -0.59 -0.46

3.4. Reflectance Difference Measurements One of the major effects on color difference after finishing can be related with surface roughness change, seen as reflectance difference ΔR between the percentage reflectance of treated fabrics from the one of control fabrics, as indicated in Figure 7. As Figure 7 shows, the DWR, DWOR and FWOR finishes have similar curves of reflectance which stabilize after 530 nm around an almost constant level.It is shown that the finishing treatment changes the percentage reflectance values of the fabric, depending on the chemical type: samples treated with chemicals that are smaller in particle size (DWOR, FWOR)generally give higher reflectance (%) values for λ>530nm; DWOR and FWOR finishes increase their refractive index, in comparison with the fabric itself, and this behaviour is opposite to the one of DWR. Samples treated with DWR finishing, having greater particle size, exhibit in fact a significant decrease in reflectance (%), especially for short wavelengths, if compared with control fabrics.This pronounced decrease may be related to the height of the surface roughness, which can scatter wavelength of the visible spectrum. The contribution of the particle size

40


distribution and the assignment of the height profile of a treated fabric surface may be correlated to the profile of the reflectance difference plots of the samples [13].

Figure 6. Color differences on cotton fabrics.

Figure 7. Reflectance differences of three finishing agents at the best concentration selected according to water and oil repellency performance results.

3.5. Absorbancemeasurements Another effect of finishing agents on color difference could be explained by the absorbance plots in the visible range as shown in Figure 8. The concentrations selected for the measurement are related with the application concentrations of the products over the textile surface.As shown in Figure 8 there are two distinct zones for each absorbance curve. The first one is approximately 350-500 nm, in which stronger adsorption of products and a higher difference between each finishing agent occur. The rate of absorbance gradually reduces and so the difference becomes smaller. This is valid under the same concentrations conditions (B, C, D: 0.50 g/L). The absorbance increases for the same product with concentration increasing (e.g. DWR A: 1.25 g/L, D: 0.50 g/L), as expected.The adsorption differences for the three


41

products are depicted in Figure 9, 10 and 11 for different colors of the same dyestuff group. Equal ratios of the dyestuff and water/product solutions were carried out for each measurement.

Figure 8. Absorbance spectrum of DWR (A: 1.25 g/L; D:0,5 g/L), DWOR (B: 0.50 g/L), FWOR (C: 0.50 g/L) solutions in the visible range.

Figure 9. Absorbance spectrum of Yellow Remazol RNL in water solution (D) and in solution with DWR (A: 1.25 g/L), DWOR (B: 0.50 g/L), FWOR (C: 0.50 g/L) products in the visible range.

Figure 10. Absorbance spectrum of Red Remazol F3B in water solution (D) and in solution with DWR (A: 1.25 g/L), DWOR (C: 0.50 g/L), FWOR (B: 0.50 g/L) products in the visible range.

42


Figure 11. Absorbance spectrum of Black Remazol B in water solution (D:0,1 g/L) and in solution with DWR (A: 1.25 g/L), DWOR (C: 0.50 g/L), FWOR (B: 0.50 g/L) products in the visible range.

For all colors there is no change in theabsorbance spectrum profile of dyestuff solution with finishing agents, but an overlay of the absorbance values in the short wavelength. This means that the dyestuffs do not interact with finishing agents but show a small variation of the λmax which results with ΔE. Absorbance values at λmax of dyestuff with water/product solutions on measurement concentrations are reported in Table 8. Table 8. Absorbance values of dyestuff with water/product solutions at λmax Absorbance Yellow Remazol RNL Red Remazol F3B Black Remazol B

Dyestuff 0.98 0.82 1.00

DWR 1.34 0.98 1.26

DWOR 0.98 0.90 1.02

FWOR 1.09 0.92 1.18

It was evaluated that red dyestuff has a lower absorbance at λmax than the other two colors. When combined with the finishing products, red dyestuff has lower influence on the increase of λmax, too. The absorbance effect of DWR is the best for all the colors, while DWOR and FWOR show similar absorbance effect except in the case of Black Remazol B. This can be related with the lower adsorption of dendrimer in comparison with fluorocarbon polymers at the same concentration. When fluorocarbon polymers dendrimers are applied, the percentage of fluorocarbon in the product decreases because the same effect of oil and water repellency is achieved with the help of the only dendrimers. That is why absorbance value is always the lowest for DWOR. Looking at absorbance values of FWOR (having only fluorocarbons)fluorocarbons polymers increase the λmax of dyestuff alone more than with dendrimers, and dendrimers alone have the lowest effect onλmax.

3.6. Color Difference Evaluation Color difference evaluation for the three tested finished, as depicted in Figure 6, could be also estimated on the base of absorbance and reflectance values considerations.For yellow (λ = 413 nm) dyed and finished cotton fabrics, the effect of absorbance for DWR is the highest,


43

when compared with all other colors. This effect is compensated for DWR lower reflectance at its wavelength, and this results in a ΔE similar to the DWOR one. FWOR finishing presents an absorbance value similar to DWOR and the highest reflectance one, so ΔE is lower.For red (λ = 541 nm) dyed and finished cotton fabrics, the absorbance effect is the lowest for all finishes, when compared with other colors. Reflectance of DWR is still quite low but absorbance is lower than the yellow case, so ΔE is the highest and decidedly higher than in yellow dyeing. For all finishes, absorbance values are quite similar, but DWOR and FWOR have an increment of ΔE, due to the reflectance contribution enhancement.For blue (λ = 600 nm) dyed and finished cotton fabrics, absorbance values are intermediate between yellow and red dyeing while reflectance values are the highest for all finishes.This provokes a fall in DWR, DWOR and FWOR ΔE values. In synthesis, for yellow and blue colors, having high values of absorbance, ΔE increases if reflectance is low, while ΔE decreases with high reflectance values. For red color, having for all finishes the lowest absorbance value and a quite high reflectance value for all finishes, a ΔE enhancement is observed.

4. CONCLUSION Textile fabrics are subjected to various treatments for water/oil repellency, for crease recovery and for a large number of different functionalities, but one of the most innovative effects could be ascribed to the color change induced by finishing operations.Hitherto, the use of dendrimers as textile dyeing auxiliaries is quite unexplored and their application is still to be optimized; in this context, dendrimer influence on color assessment is worthy of exploration.This paper has given new results associated with the evaluation of colour assessment of cotton fabric due to nanoparticle sized finishing. Color matching of dyed samples before and after repellency treatments shows an influence of finishing onto color difference.This can be due to three possible reasons: a change on the surface roughness, an influence of finishing agents concentration and a dyeing agent/dendrimer interaction or reaction. DWR, DWOR and FWOR finishes particle sizes designate the distribution and orientation of surface layer roughness and this results with color difference.The reflectance change of the treated cotton fabric seems to be related to the particle size and to the distribution of the chemical applied. In addition, it should be also taken into consideration the absorbance of finishing agents, that in the visible range influences the dyestuff λmax.Effect of surface roughness of DWR ishigher than DWOR and FWOR on color difference because of particle size distribution on the fabric surface. So it was expected to observe the highest ΔE for DWR, if taking into consideration only this major factor. As the absorbance level of DWR is not same for three colors it was clearly seen the positive effect of absorbance increasing on color difference. Increasing of λmaxafter finishing chemicals application is always positive (or there is no effect) because of an additional absorbance after applying additives over the textile surface. Although the amount of additives over the cotton surface influences additional absorbance, no interaction with dyes results with the increase on λmax. With a concentration and particle size increasing, the distribution of chemicals over the fabric causes higher surface roughness, so reflectance directly effects on concentration. Because the ability of the human eye to appreciate differences in color differs from individual to individual (as it is a combination of eye characteristics and skill of the operator), for the three different finishes

44


used ΔE1 RL=1 0

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